The erosion of bluffs lying adjacent a lake or ocean has constituted a long and serious environmental problem. These bluffs are subject to the action of the waves occasionally pounding against them which erode away the base of the bluff leaving the bluff with an extremely steep face. This steep front face is very unstable and, in some instances, is not able to support the weight of the dirt, sand and the like lying above it. Consequently, landslides or slumping may occur which can endanger man-made structures as well as trees and bushes on top of the bluff.
These bluffs as well as hillsides, such as those which slope down to a highway, are also subject, on a larger scale, to the action of forces acting within as caused by groundwater and water from spray, rain or snow melt which matriculates to various layers running through and exiting out the base of the bluffs or hillsides. If the water saturation becomes excessively high, the outwardly exerting forces cause collapse of the steep base of the bluff or hillside, sometimes along an appreciable length thereof.
One prior attempt to mitigate degradation of a hillside is disclosed in U.S. Pat. No. 4,714,376 issued Dec. 22, 1987 to Jenab. In this patent, a perforated drain pipe is placed within a hillside substantially parallel to the face of the hillside at a location on or above an impermeable layer. Jenab is primarily concerned with control of water drainage at the bottom of the hillside, and is limited to boring holes, construction of a concrete apron and placement of a drain pipe at locations close to the face of the hillside near its bottom edge where a bulldozer is used to facilitate installation. While the '376 patent discloses a use of another drain pipe at a higher level of the hillside, it is only possible that the location of such pipe is within the reaching limits of the bulldozer leading one to believe it must be near the bottom of the hillside. Installation of Jenab's drain pipes through the front face of the hillside would thus appear to contribute to the collapse of the front face of the hillside, the very problem which the present invention seeks to prevent.
Another attempt to rectify bluff erosion by controlling internal water drainage has resulted in installing wicking drains through the face of the bluff at angles generally perpendicular thereto. These installations are effected by forming a series of bores in upper elevations of the bluff using drilling equipment mounted on a support device suspended outside the face of the bluff. While such installations have been generally acceptable for their intended purpose, they have not proven to be as efficient as desired in regulating bluff drainage. They can also exacerbate the problem because they conduct water and turn many drilled holes perpendicular to the bluff which adds water to the mass between the bluff shear failure plane and the bluff face.
In view of the prior art drawbacks, applicant has developed a system and method for preventing bluff erosion as set forth in U.S. Pat. No. 6,612,778 issued Sep. 2, 2003. In this system, at least one wicking drain is positioned behind a shear failure plane and a water saturated zone or sand layer substantially parallel to the crest of the bluff or hillside for the purpose of controlling drainage of the excess water accumulation. The wicking drain extends downwardly in the bluff, laterally along and parallel to the crest of the bluff and then curves forwardly to the face of the bluff where it exits from the water saturated zone at an elevation upwardly on the face of the bluff. A collector drain pipe is connected to a distal end of the wicking drain for returning excess water accumulated in the drain to an adjacent body of water. The wicking drain is installed from the top surface of the bluff so as not to impair the structural integrity and cause land mass degradation thereof.
While this system has performed generally satisfactorily, it has been found that, in operation, the water table is at a depth in the bluff such that it has been difficult to constantly locate the wicking drain in the water saturated zone with the result that drainage has not been maximized. In addition, the wicking drain in this system extends only through a portion of the water bearing sand layer such that it somewhat limits the overall drainage of the bluff. It has also been discovered that excess tension can be placed on the wicking drain during its installation which may cause abrasion or other damage thereto and further impairs the dewatering results.
Accordingly, it is desirable to provide an upgraded system and method for preventing bluff or hillside erosion which is more efficient in stabilizing the face of the bluff or hillside by controlling the water seepage therein.